The present invention relates to a thermooptical modulator with a wave guide having a switching section, a refracting section bordering the switching section and extending transversely to the signal propagation direction in the wave guide and a first heating element extending in the refracting section along its boundary with the wave guide. A thermooptical modulator of this type was disclosed at the conference entitled "Photonics West-Optoelectronics 99" on Jan. 25, 1999 in San Jose, Calif., U.S.A. by W. Bernhard, R. Muller-Fiedler, T. Pertsch and C. Wachter. This lecture was reported after that in the Proceedings SPIE Volume 3620.
This known modulator is based on the following principle of operation. A wave guide mode is guided in a signal propagation direction to the boundary of a wave guide through total reflection. There, where the wave guide borders the refracting section, a total reflection occurs, at least on one side of the wave guide; the mode propagates in the refracting section; and no noteworthy light intensity emerges into the section of the wave guide, where it separates again from the refracting section. In its resting state this type of structure is practically impenetrable for the mode.
In order to be able to modulate the intensity of the light passing through the structure, a heating element is provided along the boundary between the wave guide and the refracting section. If this refracting section is heated in the vicinity of the boundary, the refractive index of this section is decreased, so that the mode propagates in the wave guide, also in the refracting section, and passes through the modulator without a reduction in intensity or with little intensity reduction. The transmission of the structure may thus be controlled in a simple way by turning the heating element on and off.
Polymeric material having a noteworthy or marked thermooptic effect can be used as the material for the wave guide and the bending section. A thermooptic effect means that its index of refraction changes significantly with changing temperature.
However these polymeric materials do not completely relax into their initial state after their temperature is returned to its initial value after a temperature change so that a small residual index of refraction change remains even after the temperature is returned to its initial value. Because of this residual index of refraction change a portion of the light passes through the modulator, even when the heating element is turned off. For engineering applications, especially with integrated optical circuits for optical telecommunications networks, however a rapid and complete suppression of the signal to be modulated and a rapid and complete shut off of the modulator are required.